LeetCode面试题 17.24. Max Submatrix LCCI——压缩数组+动态规划

一、题目

Given an NxM matrix of positive and negative integers, write code to find the submatrix with the largest possible sum.

Return an array [r1, c1, r2, c2], where r1, c1 are the row number and the column number of the submatrix’s upper left corner respectively, and r2, c2 are the row number of and the column number of lower right corner. If there are more than one answers, return any one of them.

Note: This problem is slightly different from the original one in the book.

Example:

Input:
[
[-1,0],
[0,-1]
]
Output: [0,1,0,1]
Note:

1 <= matrix.length, matrix[0].length <= 200

二、题解

class Solution {
public:
    vector<int> getMaxMatrix(vector<vector<int>>& matrix) {
        int n = matrix.size(),m = matrix[0].size();
        int maxVal = INT_MIN;
        int a = 0,b = 0,c = 0,d = 0;
        for(int up = 0;up < n;up++){
            vector<int> nums(m,0);
            for(int down = up;down < n;down++){
                for(int l = 0,r = 0,pre = INT_MIN;r < m;r++){
                    nums[r] += matrix[down][r];
                    if(pre > 0) pre += nums[r];
                    else {
                        pre = nums[r];
                        l = r;
                    }
                    if(pre > maxVal){
                        maxVal = pre;
                        a = up;
                        b = l;
                        c = down;
                        d = r;
                    }
                }
            }
        }
        return {a,b,c,d};
    }
};